If you have it endorsed on your UK licence it should transfer to your Australian licence (??)
As long as you can show that you have done the dual instruction (10 hours for a night rating) and then a test, then the night rating becomes perpetual (I think).
Not so with the instrument rating. Must do a test when you arrive in country to have that endorsed.
CASA has a pretty good website. Look up the CAO's on the the web and search night rating.